Preliminary results in this laboratory applying the techniques outlined for the proposed investigation have shown that: 1) primitive otoconia originate from segmentation of an immature otolithic membrane, and 2) that calcium granules (20-150 nm in diameter) first become attached to the external surface of the primitive otoconia and are subsequently incorporated into the organic matrix. The proposed study intends to expand these findings in order to fully investigate the progression of these processes in time and space (age/location). The study intends to characterize the morphological changes that culminate with the differentiation and maturation of chick embryo otoliths by: 1) analyzing the details of the segmentation process of the immature otolithic membrane, 2) analyzing the relationship that exists between the organic matrix and the mineral components, i. e., origin, migration and distribution of the calcium containing granules, and 3) analyzing the differentiation and maturation of the macular epithelia in the vestibular labyrinth. A morphological correlation between the maturation of the otoliths and the macular epithelia, with special emphasis on synaptogenesis at each stage, will be carried out. Twelve different ages between 3-21 days of incubation (stages 15-46) will be examined. Light and electron microscopy histochemistry will be used and serial thick and thin sections of the maculae will be obtained in order to determine the regional changes that probably result in different developmental gradients for each macula. The otoliths provide indispensable cues for sensory perception and physical orientation to the environment. Although abnormality of the vestibular nerve and nuclei contribute to postural imbalance and ataxia, the otolithic end organs provide the primary input for gravitational detection. Without the otoliths vertebrates have great difficulty keeping body balance. Nonetheless, little is known about their development. We must fully understand the normal development of the otoliths before we can begin to understand the changes that genetic deficits and teratogens produce in the embryonic ear.